Ok this is possibly the easiest thing on earth but I didn’t see any clear documentation on the topic apart from a simple text file which actually helped.
The server runs into a FreeBSD jail, I won’t cover this part as there are plenty of good documentation on this matter already.
The first step is obviously to install nsd, for example using pkg:
# pkg install nsd My master DNS server runs BIND so there’s no specifics regarding nsd, here’s the most basic configuration the slave needs: